Switching apparatus

ABSTRACT

In a switch each pole comprises a movable contact pivoted at the outer end of an arm the inner end of which is pivoted on a fixed block about a fixed pivoting axis, while being longitudinally slidable thereon. A spring urges the movable contact both angularly in the same direction as the direction of the opening angular movement of the arm about is pivoting axis, and radially and outwardly with respect to said axis, angular rotation of the movable contact with respect to the arm under the action of the spring being limited by an abutment. During the closing movement of the arm, cam surfaces act on the arm actuating member to push the said arm inwardly with respect to its pivoting axis against the spring. At the end of this movement the cam surfaces liberate the arm actuating member and the movable contact is thus suddenly applied by the spring against a fixed contact. During the subsequent opening movement of the arm, the cam surfaces are rendered ineffective and the movable contact is momentarily retained by the fixed contact owing to the conformation of the contacting surfaces. It is thus compelled to rotate against the action of the spring until it is fully disengaged from the fixed contact. The movable contact may be equipped with an auxiliary arc rupturing contact which forms a fulcrum for the rotation of the movable contact.

United States Patent lnventor Marcel Duza Primary Examiner-Robert S. Macon 125 rue Garibaldi, 69 Lyon, Geme, France Assistant Examiner- William J. Smith Appl. No. 843,960 Anorney-Alexander & Dowell Filed July 23, 1969 Patented Feb. 16,1971 Priority Aug. 5, 1968 ABSTRACT: In a switch each pole comprises a movable con- France tact pivoted at the outer end of an arm the inner end of which 50,275 is pivoted on a fixed block about a fixed pivoting axis, while being longitudinally slidable thereon. A spring urges the movable contact both angularly in the same direction as the direction of the opening angular movement of the arm about its pivoting axis, and radially and outwardly with respect to said axis, angular rotation of the movable contact with respect to the arm under the action of the spring being limited by an SWITCHING APPARATUS abutment. During the closing movement of the arm, cam sur- 90mm, 12 Drawing 518$ faces act on the arm actuating member to push the sa d arm inwardly with respect to its pivotmg axis against the spring. At [1.8. CI. the end of this movement the cam urfaces liberate the arm 200/ 146, 200/15 actuating member and the movable contact is thus suddenly ll!- Clthe spring against a fixed ontact During the ub. Fleld ofsealch 74, sequent opening movement of the arm the cam surfaces are 153-1 1, 146 rendered ineffective and the movable contact is momentarily References Cited retained by the fixed contact owing to the conformation of the contacting surfaces. It is thus compelled to rotate against the UNITED STATES PATENTS action of the spring until it is fully disengaged from the fixed 1,189,276 7/ 1916 Mahoney et al. 200/ 146 contact. The movable contact maybe equipped with an aux- 7/l9l6 Aalborg et al. 200/146 iliary arc rupturing contact which forms a fulcrum for the 2,937,258 5/1960 Starr 200/74(X) rotation of the movable contact.

5 C 3 4L I 5d. 1 a i 5 4 s l 154. D 4

PATENT'ELD Fm SIS?! V 356 41 sum 2 [IF 3 v PATENTEU FEB] m] 55 -1 saw 3 if-3 1 SWITCHING APPARATUS The present invention relates to electric switching apparatus.

An essential condition required from such apparatus is that their contact resistance should be practically negligible in continuous operation under the highest'admissible current. For this purpose the contacting surfaces should be relatively large and the contacting pressure should be relatively high. Such is the case for instance with switches of the type comprising a movable member, such as a blade, which slides against fixed surfaces such as the inner sides of a resilient jaw. The disadvantage of these switches is that important frictional forces appear between the movable member and the fixed surfaces, and that therefore the force or torque required for proper actuation of the switch is relatively high] v v It is an object of the present invention to provide a switching apparatus wherein sliding contact surfaces are almost completely eliminated.

Another object of this invention is to provide a switching apparatus wherein the erosion of the contacting members also realizes a quick movement of the movable contacts and it is so arranged that when it comprises two poles or more, the movable parts of these poles maybe actuated simultaneously while'being sufficientlyindependent from each other in order that manufacturing tolerances may have no effect on the contacting pressure developed in the individual poles. 1

In accordance with the present invention a switching apparatus comprises for each pole a fixed contact, a movable contact adapted for cooperation with this fixed contact, an arm to the free'end of which the movable contact is pivoted,

the angular displacement of the latter with respect to the said arm being limited by appropriate abutments, a fixed supporting member on which the said arm is rotatablymo'unted while being radially slidable thereon, and a spring tending to urge the movable contact radially and outwardly with respect to the said supporting member, in such manner that the spring, the arm and the movable contact form an'elastically extensible articulated overcenter or toggle mechanism interposed between the supporting member and the fixed contact, while the simultaneous actuation of all the individual mechanisms corresponding tothe poles of the apparatus is effected by means of a single actuating member acting on the arm of each mechanism so as to rotate the arm .of the latter, the said actuating member cooperating with a fixed cam surface for pushing each arm radially towards its supporting member, when the apparatus is being closed, to permit free displacement of the movable contact until same is situated in front of the corresponding fixed contact, and then for liberating the said arm in order that its movable contact may be applied tending to bring the movable parts to the end of their opening stroke.

An auxiliary contacting finger or plate is preferably associated with each movable contact to cooperate with a corresponding portion of the fixed contact in such manner as to form a fulcrum for the movable contact and for the overcenter or toggle mechanism when the apparatus is being opened. This auxiliary contacting finger may also act as a quick-break are rupturing contact, if desired.

In the annexed drawings:

FIG. I is a general longitudinal section of a switching apparatus according to this invention.

FIG. 2 is a side view thereof, the front lateral wall of the casing being supposedly removed.

FIG. 3 is a fragmental section taken along line IlI-lll of FIG. 2, this FIG. indicating respectively at H and 11-" the lines of section corresponding to FIGS. 1 and 2.

FIG. 4 is a fragmental section taken along line IV-IV of FIG. 2.

FIG. 5 is a perspective view showing the slidable guiding clamp provided at the inner endof the flexible conducting ribbon corresponding to a pole of the apparatus.

FIG. 6 is a general perspective view of the apparatus.

FIG. 7 is a small scale longitudinal section similar to FIG. 1,

- but illustrating the parts during the opening movement of the -wall supposedly removed as in FIG. 2, but showing the parts at the position illustrated in FIG. 7. v

FIGS. 9 and 10 are views respectively similar to FIGS. 7 and 8, but showing the parts at the open position.

FIGS. 11 and 12 are also views similar to FIGS. 7 and 8, but the parts being illustrated somewhat before the end of the closing movement of the switch.

Referring to FIGS. 1 to 3, the switching apparatus illustrated comprises an insulating boxlike casing having an open upper end. .Starting from the left in FIG. I, the lateral upper edge of easing 1 comprises a horizontal portion 1a followed by a downwardly inclined portion lb.'In the vicinity of the lefthand end of the horizontal portion In casing 1 supports a transverse rod 2 FIGS. 1 and 2) on which an actuating lever 3 is rotatably mounted. The forked free end of this lever in turn .carries another transverse rod 4 (FIG. 3) the ends of which are slidable in Iongitudinal slots Sa' (FIG. 2) formediinthe flat branches of the bifurcated freeend of another lever 5 which is in turn pivoted on'a transverse rod 6 mounted in the lateral walls of easing 1 near the right-hand end of the slanting portion 1b of the upper edge thereof. Lever 5 extends beyond rod 6 in the form of a nose 5b adapted to bear against the lateral wall of casing l to limit clockwise rotation of this lever during the opening movement of the switch, as more fully explained below. Lever 5 further carries an actuating head or handle 5c (see FIG. 6) obliquely disposed above its end opposed to rod 6, this handle being connected with lever 5 by a vertical web 5d (FIG. 2) in such manner as to be operatable in both directions (downwardly or upwardly).

against the corresponding fixed contact under the action of v the spring, the said cam surface being so arranged as to become ineffective when the switch is being opened.

The fixed contacts and the movable contacts are preferably so formed as to fit into each otherat the closed position of the switch, their longitudinal profile being however such that they may be readily disengaged from each other by rotation and contraction of the articulated overcenter mechanism against the action of its spring.

In order to limit the radial outward displacement of the arms with respect to their supporting members when the switch is being opened the actuating member is preferably retained by fixed cam surfaces and these surfaces are conveniently so shaped as to determine a reaction component An actuation member 7, generally formed as a connecting rod, is rotatably mounted on rod 4 between the flat branches of both levers 3 and 5. This actuating member, made of an appropriate insulating material, comprises an upper hub portion 7a which surrounds rod 4 (FIG. 3) and this hub is formed, for each pole of the switch, with a downwardly directed bifurcated extension the branches of which are disposed on each side of the movable parts corresponding to the said pole. The switch illustrated being of the three-pole type, the branches of the extension corresponding to the central pole have been referenced 7b in FIG. 3. As to the lateral poles, each extension has an inner branch 7b similar to those of the central pole, and an outer branch 70 of somewhat greater length, this branch 70 carrying a horizontal pin 8 which extends towards the adjacent lateral wall of easing 1. The protruding portion of pin 8 rotatably carries a roller 9 movable in a flat recess or depression 1c formed in the inner side of the said lateral wall. As

shown in FIG. 2 each recess is of generally upwardly flaring shape.

- In .FIG. 3 reference numeral 1d designates a partition integral with the bottom of casing l and adapted to separate the central pole from the lateral one illustrated in FIG. 3.

. Each pole assembly comprises a contact carrying arm of generally inverted U-shaped cross section as shown in FIG. 3, the upper horizontal web being referenced 10a. It is to be noted that this horizontal web only extends in the central portion of arm 10. In the vicinity of the right-hand end of arm 10 the vertical branches thereof have each of longitudinally elongated rectangular opening 10b. Each opening 10b slidably receives twosuperposed lugs 11a (FIGS. 4 and 5) which extend laterally from the flat branchesof a clamp 11 made of folded sheet metal, in which is disposed one end of a conducting braided ribbon 12. The back or fold of this clamp is of rounded cross section as indicated at 11b in FIG. 5, in such manner as to bear in a groove 13a '(FlG. l) of arcuate cross section provided inthe vertical side of a fixed metallic block 13 which forms one of the terminals of the pole under consideration. Block 13 is secured to the bottom of the insulating casing 1 by means of a screw- 14, while reference numeral 15 designates the conventional screw adapted to clamp the end of I a wire 16 in a perforation of block 13.

' It will further be noted that clamp 11 and ribbon 12 have a central hole 110 (FIG. 5) to receive one end of a wire spring 17 (FIG. 1) as more fully explained below.

The end of arm 10 opposed to block 13 carries a transverse pin, vl8 (FIG. 1) which rotatably supports a massive movable contact 19. Below pin 18 this con'tac't'is formed with a recess 19a opening towards the right (i.e. towards block 13) and into which is engaged the otherend of the above-mentioned spring 17. Spring l7 is made of a downwardly curved steel wire and its end engaged through the hole 11c of clamp 11 is formed as a hook inorderto be retained in position. This spring urges apart movable contact 19 and clamp 11 and it also tends to rotate contact 19 in the clockwise direction. The second end of the conducting ribbon 12 is applied against the upper side of contact 19 by an elongated plate or finger 20 secured by screws 21. This plate extends longitudinally beyond contact 19 in both directions, its right-hand end being adapted to bear against the above-mentioned web 101; in order to limit the clockwise rotation of contact 19 underthe action of spring 17.

The movable contact 19 cooperates with a fixed contact or block 22 secured to the bottom of easing l by a screw23. Block 22 forms thesecond terminal of the pole under consideration and it is providedfor this purpose with a screw 24 adapted to clamp the end of a wire such as 25. As illustrated in FIG. 1 at the closed position of the switch contacts 19 and 22 engage each other along two contacting planes A and B, the former being inclined in such a direction with respect to the radii from the center of groove 13a, that when arm 10 rotates in the opening direction (i.e. clockwise in FIG. 1) this plane tends to push contact 19 towards the said center. As to plane 8, it is inclined in the reverse direction at a relatively small angle with respect to the radii. Block 22 is further fonned with pose it overlaps the left-hand edge of the corresponding depression or recess 10.

v For a clearer description of the operation it will first be supposed that the switch is of the single-pole type.

At the closed position of FIGS. 1 and 2, the movable contact 19 is strongly applied against the fixed contact or block 22 by spring 17, the contacting surfaces corresponding to planes A and B of FIG. 1. This position is perfectly stable since any small rotation of arm 10 in any direction would tend to urge contact 19 towards the center of groove 130 (which forms the center of rotation of arm 10) against the reaction of spring 17. It will be noted that at this position rollers 9 are situated below sectors 27 which are therefore ineffective.

In order to open the switch it is therefore necessary to pull upwardly the head or handle 5a of lever 5 (see FIG. 6). This pull is transmitted to the actuating member 7 which raises pin 26 and therefore arm 10. The movable contact 19 must rotate counterclockwise at the end of arm 10; the outer end of plate 20 bearing against recess 220 which actsas a fulcrum (after a quite small initial rotation of said contact 19 about the upper 3 edge of plane A, since in practice the outer end of plate 20 they raise sectors 27 against the action of springs 29. The parts I then assume the position illustrated in FIGS. 9 and 10. It will an upper recess 22a adapted to receive the curved outer end of the elongated plate 20.

A transverse pin 26 (FIGS. 1 and 3) is passed through the lateral sides of arm 10, the protruding ends of this rod being disposed in flat recesses or depressions 7d formed in the inner sides of the branches 7b and/or 7c of the extension of actuating member 7 which corresponds to the pole under consideration. As shown in dotted lines in FIG. 2 these recesses have a triangular profile opening along the'edge of member 7 which faces block 13 (right-hand edge in FIG. 2).

A sector 27 (FIGS. 2 and 3) is disposed against the inner side of each of the lateral walls of easing 1 to cooperate with the adjacent roller 9. This sector is pivoted on a pin 28 carried reach the position illustrated in FIGS. 7 and 8 at which recess 22a, pin 18 and groove are in line. However this position does not exactly correspond to the position of unstable equilibrium of the toggle mechanism because spring 17 acts on movable contact 19 below pin 18 and therefore exerts a torque on contact 19. But since recess 19a is close to pin 18, this torque is small and therefore it may be considered that this position of unstable equilibrium is reached very slightly after the position illustrated in FIGS. 7 and 8 and that afterwards spring 17 tends to rotate-arm 10 clockwise, i.e. in the opening direction.

As soon as the rounded outer end of plate 20 is disengaged from recess 22a, the toggle mechanism is free to expand. Rotation of movable contact 19 under the action of spring 17 is limited by the inner end of plate 20 abutting against web 10a. As to the outward displacement of arm 10, pin 16 and actuating member 7 towards the left in FIG. 1, it is stopped by rollers 9 abutting against the left-hand edge of recesses 1c of easing 1. Since these edges then correspond forarrn 10 to a line of increasing radius with respect to groove 13a, the reaction applied to rollers 9 tends to assist clockwise rotation of arm 10, this rotation continuing until nose 5b abuts against the corresponding portion of the upper edge of easing 1. The parts be noted that at this position rollers9 have liberated sectors 27 which have been returned to their position of rest by springs 29. t

The movable contact 19 has been fully separated from the fixed contact 22. But the electric'connection between both contacts has been maintained during a short time by plate 20 (see position of FIGS. 7 and 8) and thereafter the circuit has been suddenly opened when plate 20 has become disengaged from recess 22a. Plate 20 thus acts as a quick-acting arc rupturing finger. Frictional forces have been practically eliminated and in any case they do not appear between the main contacting surfaces (planes A'and B of FIG. 1).

In order to close the switch the operator pushes the head or handle 50 of FIG. 6. The movable-parts are then displaced in the reverse direction'with respect to the opening operation, but in this case rollers 9 engage the cam surfaces formed by the periphery of sectors 27 which are then applied downwardly against the bottom'of casing 1 and cannot be set aside by counterclockwise rotation as explained with reference to FIG. 8. The actuating member 7 is therefore pushed towards the right in FIG. 1 and the toggle mechanism -19-18-10-22a is thus contracted through pin 26. The movable contact 19 together with its associated plate 20 are displaced longitudinally towards the right until rollers 9 reach the lower end of sectors 27 (position of FIGS, 11 and 12). Shortly before the end of the downward stroke of member 7 (as determined by rollers 9 reaching the bottom of depressions 1c) these rollers 9 leave the periphery of sectors 27 and member 7 is free to move towards the left together with pin 26, arm 10, contact 19 and plate 20. The parts thus reassume suddenly the position illustrated in FIGS. 1 and 2 under the action of spring 17.

It results from the preceding explanations that the arrangement described ensures a quick opening and a quick closing of the electric circuit corresponding to the pole under consideration. In other words it may be said that the switchcis of the socalled quick make and break" type.

ln the preceding explanations it has been supposed that the switch only comprised a single pole, but is is now easy to understand that the general operation remains quite the same for a multipolar apparatus. During the opening step all the toggle mechanisms are liberated substantially at the same time, while during the closing step all the movable contacts 19 are released exactly in unison whenrollers'9 escape the lower end of the periphery of sectors 27 and therefore the poles are closed simultaneously.

lclaim:

1. An electric switching apparatus comprising a fixed conducting block',

a contact-carrying arm having an inner end and an outer end, with said inner end being pivotally connected with said conducting block about a fixed pivoting axis and being slidable with respect to said block longitudinally of said arm and radially of said axis;

a movable contact pivoted to the outer end of said contact carrying arm;

current carrying means interposed between said movable contact and said block;

a fixed contact to cooperate with said movable contact, said movable contact and said fixed contact defining for the angular movement of said arm about said pivoting axis a closing direction for which said movable contact is brought into engagement with said fixed contact, and an opening direction for which said movable contact is disengaged and separated from said fixed contact;

spring means acting on said movable contact to urge same radially from said pivoting axis and also to tend to rotate same on the outer end of said arm in the same direction as the opening direction of the angular movement of said arm about said pivoting axis;

means to limit angular movement of said movable contact with respect to said arm under the action of said spring means;

means to actuate said arm in the closing and in the opening direction of the angular movement thereof about said pivoting axis, between a closed position for which said movable contact is fully engaged with said fixed contact and an open position for which said movable contact is fully separated from said fixed contact; and

cam means operative when said arm is actuated between said open position and said closed position in the closing direction of the angular movement thereof about said pivoting axis, to push said arm radially against the action of said spring means so as to move said movable contact towards said pivoting axis until said movable contact is in front of said fixed contact. and then to suddenly liberate said arm to cause said movable contact to engage said fixed contact under the action of said spring means, said cam means being inoperative when said arm is actuated in the opening direction about said pivoting axis between said closed position and said open position.

2. In a switching apparatus as claimed in claim 1. said fixed contact and said movable contact being formed with cooperative contacting surfaces which are uniformly applied against each other at the closed position of said contact carrying arm, with a portion of said contacting surfaces being so shaped that when said arm is actuated in the opening direction about said pivoting axis between its closed and its open position, said movable contact is caused to rotate against said spring means on the outer end of said arm in the same direction as the closing direction of the angular movement of said arm about said pivoting axis in order to effect disengagement of said movable contact from said fixed contact.

3. In a switching apparatus as claimed in claim 1, an arc rupturing finger secured to said movable contact, said finger having an outer end engaging said fixed contact at the closed position of said contact carrying arm; and said fixed contact being formed with a recess to receive the outer end of said finger and to form a fulcrum for said finger when said arm is actuated in the opening direction about said pivoting axis between its closed position and its open position, in order to cause rotation of said movable contact on the outer end of said arm in the same direction as the closing direction of the angular movement of said arm about said pivoting axis, and to thus effect disengagement of said movable contact from said fixed contact.

4. In a switching apparatus as claimed in claim 1, said cam surfaces comprising at least one sector pivoted about an axis substantially parallel to the pivoting axis of said contact carrying arm, cam follower means carried by said arm actuating means to cooperate with the periphery of said sector when said arm is actuated in the closing direction about said pivoting axis between its opened and its closed position, a fixed abutment to retain said sector against rotation under the action of said cam follower means on the periphery of said sec-- tor, and biassing spring means urging said sector against said abutment, said cam follower means escaping the periphery of said sector when said arm reaches its closed position, and said cam follower means displacing said'sector against the action of said biassing means, without engaging the periphery of said sector, when said arm is actuated in the opening direction about said pivoting axis between its closed position and its open position.

5. In a switching apparatus as claimed in claim 4, auxiliary fixed cam surfaces cooperating with said cam follower means to limit outward radial displacement of said contact carrying arm with respect to the pivoting axis thereof, said auxiliary cam surfaces corresponding to a curve the successive points of which are at an increasing radial distance from the pivoting axis of said arm in the opening direction of the angular movement of said arm about its pivoting axis.

6. In a switching apparatus as claimed in claim 1, said contact carrying arm being formed at its inner end with a longitudinally elongated slot, said fixed block having a rounded recess concentric to said pivoting axis of said arm and opening toward said arm, said apparatus further comprising an intermediate member having portions longitudinally slidable in said elongated slot and formed with a rounded terminal portion rotatablydisposed in said rounded recess, and said spring means being interposed between said movable contact and said intermediate member.

7. In a switching apparatus as claimed in claim 6, said contact carrying arm being of bifurcated shape with two substantially fiat parallel branches at its outer end and at its inner end, with said longitudinally elongated slot being formed in both branches at the inner end of said arm, said intermediate member being in the form of a clamp disposed between the branches of said arm at the inner end thereof and being formed with lateral lugs slidable in said slots, said movable contact being disposed between the branches of said arm at the outer end thereof, and said current carrying means including a fiat conducting ribbon having a first end secured to said movable contact and a second end retained by said clamp.

8. ln a switching apparatus as claimed in claim 7. said spring means being in the form of a resilient wire having a first end acting on said movable contact and a second end acting on said clamp.

9. In a switching apparatus as claimed in claim 1, said arm actuating means including a bifurcated actuating member having its branches disposed each side of said contact carrying arm, with each of said branches having an inner side formed said arm and protruding on eaai side thereof into the depression of the adjacent branch of said actuating member to form a mechanical connection between said actuating member and said arm. 

1. An electric switching apparatus comprising a fixed conducting block; a contact-carrying arm having an inner end and an outer end, with said inner end being pivotally connected with said conducting block about a fixed pivoting axis and being slidable with respect to said block longitudinally of said arm and radially of said axis; a movable contact pivoted to the outer end of said contact carrying arm; current carrying means interposed between said movable contact and said block; a fixed contact to cooperate with said movable contact, said movable contact and said fixed contact defining for the angular movement of said arm about said pivoting axis a closing direction for which said movable contact is brought into engagement with said fixed contact, and an opening direction for which said movable contact is disengaged and separated from said fixed contact; spring means acting on said movable contact to urge same radially from said pivoting axis and also to tend to rotate same on the outer end of said arm in the same direction as the opening direction of the angular movement of said arm about said pivoting axis; means to limit angular movement of said movable contact with respect to said arm under the action of said spring means; means to actuate said arm in the closing and in the opening direction of the angular movement thereof about said pivoting axis, between a closed position for which said movable contact is fully engaged with said fixed contact and an open position for which said movable contact is fully separated from said fixed contact; and cam means operative when said arm is actuated between said open position and said closed position in the closing direction of the angular movement thereof about said pivoting axis, to push said arm radially against the action of said spring means so as to move said movable contact towards said pivoting axis until said movable contact is in front of said fixed contact, and then to suddenly liberate said arm to cause said movable contact to engage said fixed contact under the action of said spring means, said cam means being inoperative when said arm is actuated in the opening direction about said pivoting axis between said closed position and said open position.
 2. In a switching apparatus as claimed in claim 1, said fixed contact and said movable contact being formed with cooperative contacting surfaces which are uniformly applied against each other at the closed position of said contact carrying arm, with a portion of said contacting surfaces being so shaped that when said arm is actuated in the opening direction about said pivoting axis between its closed and its open position, said movable contact is caused to rotate against said spring means on the outer end of said arm in the same direction as the closing direction of the angular movement of said arm about said pivoting axis in order to effect disengagement of said movable contact from said fixed contact.
 3. In a switching apparatus as claimed in claim 1, an arc rupturing finger secured to said movable contact, said finger having an outer end engaging said fixed contact at the closed position of said contact carrying arm; and said fixed contact being formed with a recess to receive the outer end of said finger and to form a fulcrum for said finger when said arm is actuated in the opening direction about said pivoting axis between its closed position and its open position, in order to cause rotation of said movable contact on the outer end of said arm in the same direction as the closing direction of the angular movement of said arm about said pivoting axis, and to thus effect disengagement of said movable contact from said fixed contact.
 4. In a switching apparatus as claimed in claim 1, said cam surfaces comprising at least one sector pivoted about an axis substantially parallel to the pivoting axis of said contact carrying arm, cam follower means carried by said arm actuating means to cooperate with the periphery of said sector when said arm is actuated in the closing direction about said pivoting axis between its opened and its closed position, a fixed abutment to retain said sector against rotation under the action of said cam follower means on the periphery of said sector, and biassing spring means urging said sector against said abutment, said cam follower means escaping the periphery of said sector when said arm reaches its closed position, and said cam follower means displacing said sector against the action of said biassing means, without engaging the periphery of said sector, when said arm is actuated in the opening direction about said pivoting axis between its closed position and its open position.
 5. In a switching apparatus as claimed in claim 4, auxiliary fixed cam surfaces cooperating with said cam follower means to limit outward radial displacement of said contact carrying arm with respect to the pivoting axis thereof, said auxiliary cam surfaces corresponding to a curve the successive points of which are at an increasing radial distance from the pivoting axis of said arm in the opening direction of the angular movement of said arm about its pivoting axis.
 6. In a switching apparatus as claimed in claim 1, said contact carrying arm being formed at its inner end with a longitudinally elongated slot, said fixed block having a rounded recess concentric to said pivoting axis of said arm and opening toward said arm, said apparatus further comprising an intermediate member having portions longitudinally slidable in said elongated slot and formed with a rounded terminal portion rotatably disposed in said rounded recess, and said spring means being interposed between said movable contact and said intermediate member.
 7. In a switching apparatus as claimed in claim 6, said contact carrying arm being of bifurcated shape with two substantially flat parallel branches at its outer end and at its inner end, with said longitudinally elongated slot being formed in both branches at the inner end of said arm, said intermediate member being in the form of a clamp disposed between the branches of said arm at the inner end thereof and being formed with lateral lugs slidable in said slots, said movable contact being disposed between the branches of said arm at the outer end thereof, and said current carrying means including a flat conducting ribbon having a first end secured to said movable contact and a second end retained by said clamp.
 8. In a switching apparatus as claimed in claim 7, said spring means being in the form of a resilient wire having a first end acting on said movable contact and a second end acting on said clamp.
 9. In a switching apparatus as claimed in claim 1, said arm actuating means including a bifurcated actuating member having its branches disposed each side of said contact carrying arm, with each of said branches having an inner side formed with a substantially flat V-shaped depression opening towards said pivoting axis of said arm, and a transverse pin carried by said arm and protruding on each side thereof into the depression of the adjacent branch of said actuating member to form a mechanical connection between said actuating member and said arm. 